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Emails from UPS(nut) is sent with extra mail headers that ISP blocks

Apr 17, 2018
I have set up Email on the web-gui with a ISP that hosts my domain and email, a typical authenticated smtp, port 587 with STARTTLS with a valid sender address. When I configured the Email on the web-gui the test mail worked perfectly, however the UPS(nut) emails are being blocked with smtp error 550 due to two headers that are added for email sent by UPS(nut). When UPS sends emails it calls the script "/usr/local/bin/custom-upssched-cmd EMAIL" that uses the "mail" program to send email.
The headers added are:
X-Mailer: FreeNAS

Is there a way to avoid mail/sendmail from adding these two headers?
If not, then it might be a good idea to change email sending method to the same as used on the web-gui test email. That way if the test mail works, then all email notification work.
Aug 22, 2012
I know this isn't the solution you want to hear, but the easiest solution to this would be to set up an account at some other email host.

What's the error message that you're getting?
Could you talk to the ISP and find out why they think those headers are worth blocking?
Is the message blocked from being received or blocked from being sent? I suppose SMTP indicates they're blocked from sending.

You could probably set up a jail with an SMTP server that just relays the messages after stripping out those headers. I was recently looking at doing this and there are some very simple Python libraries you could use.